Heat exchange apparatus



Y spf.15,j1959. [1Km/IES En; l2,904,013

. v HEAT ExHANGE APxARA'Tujs Filed May s, 1954 4 sheets-sheet 1 ATTORNEY Sept. 15, 1959 b. K. DAVIES ETAL v 2,904,013

' HEAT EXCHANGE APPARATUS Filed May 6, 1954 4 Sheets-Sheet 2 l ATTORNEY 4 Sheets-Sheet 3 D. K. vmAvuas vETAI.V HEAT EXCEANGE APPARATUS HWY@ sepf. 15, 1959 Filed lla-.Y v6, 1954 ATTORNEY Sept 15,1959 'I in. K.DAv|EsgvE1-AL 2,904,013

HEAT EXCHANGE APPARATUS rileduaye, 1954 K A 4 sheets-sheet 4 ATTORNEY United States Patent O HEAT EXCHANGE APPARATUS David K. Davies and Earl E. Schoessow, Barberton, Ohio, assignors to The Babcock & Wilcox Company, New York, N.Y., a corporation of New Jersey Application May 6, 1954, Serial No. 428,038

4 Claims. (Cl. 122-32) The present invention relates in general to the construction and operation of heat exchange apparatus, and more particularly to 'vapor generating units which are expecially designed for service with a high temperature and pressure corrosive heating fluid which is subject to very rapid changes in temperature during operation and which must be maintained relatively uncontaminated by uid leakage or products of corrosion.

It has heretofore been known to construct the fluid contacting parts of heat exchangers utilizing one or more corrosive fluids entirely of austenitic stainless steels. Since austenitic steels have a considerably higher coefficient of thermal expansion than carbon steel, it has been considered impractical to construct coextensive connected parts of such heat exchangers of such diiferent metals to reduce the total cost, in as much as the austentic steels are approximately live times the cost of carbon steels. Austenitic steels are also objectionable for heat exchanger parts because of their lovtr resistance to thermal shock. It is also difficult to fabricate large diameter thick plate required for high pressure tube sheets of austenitic stainless steels.

Where non-contaimination of a uid at high temperatures and pressures is required in a heat exchanger, the normal practices of using floating heads, packed tube joints, and expansion joints are not sufficient to satisfy the stringent leakage requirements and a welded or integral connection of the tubes to the tube sheets and of the tube sheets to the shell is required. Where a welded construction of thick pressure parts is required, austenitic stainless steels are objectionable because of their poor welding characteristics.

Heat exchangers having a single tube sheet divided by an associated partition into inlet and outlet sections, a bank of U-shaped tubes extending between and connected to the inlet and outlet sections, and a single shell encompassing the tube sheet and tube bank, are well born. While this construction permits differential thermal expansion between the tubes and the shell, it is undesirable when large, e.g. 150 F. temperature differences exist between the heating fluid and the cooling or heated fluid. Such temperature differences tend to cause distortion in the shell and tube sheet and frequently result in failure of the heat exchanger. i'

The main object of this invention is the provision of heat exchange apparatus having a construction capable of safely withstanding the thermal stresses due to differential expansionof the fluid contacting parts, su'ch as a tube bank and enclosing shell, resulting from one of the fluids being at a high temperature and pressure. A further object is the provision of heat exchange apparatus of the character described designed for vservice with a'corrosive lheating fluid at a high temperature-and pressure and wherein contamination of the heating uid .is avoided. A further object is the provisionv of heat exchange apparatus designed for service conditions in which substantiallyrall of the heat is supplied by a cor- :rosive iiuid at ay high temperaturev and pressure and "ice which is characterized by its low space requirements,

striction of the thermal stresses between its componentI fluid contacting parts to safe operating limits.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention, its operating advantages and speciic objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invnetion.

Of the drawings:

Fig. l is an elevation of a vapor generating unit constructed `in accordance with the present invention;

Fig. 2 is an end View of the vapor generating uni-t shown in Fig. l;V

Fig. 3 is a plan section of the U-shaped heat exchanger section of the vapor generating unit shown in Figs. l and 2;

Fig. 4 is a vertical transverse section taken on the line 4-4 of Fig. 3;

Fig. 5 is a fragmentary section taken on the line 5--5 of Fig. 4; v

Fig. 6 is a vertical transverse section taken on the line 6 6 of Fig. 3;

Fig. 7 is a fragmentary section taken on the line 7-7 of Fig. 6; and

Fig. 8 is a fragmentary section showing the tube attachment to the tube sheet.

In the drawings we have illustrated a steam generating unit designed for high pressure-high temperature service constructed in accordance with the invention and comprising a horizontally arranged elongated vapor-liquid separating drum 10, a horizontally arranged U-shaped heat exchanger 14 symmetrically arranged below the drum, and riser tubes 16 and downcomer tubes 18 extending between the drum and the heat exchanger and connected thereto. The heat exchanger 14 is supported by longitudinally spaced groups of pedestal supports 20A and 20B, the heat exchanger being secured in the forward group 20A and arranged to slide in the after group 20B while being restrained in a Vertical direction. The drum 10 is supported in longitudinally spaced saddle supports 22A and 22B, the drum being secured to the saddle 22A and being arranged to longitudinally expand in -the saddle 22B while being restrained in the vertical direction. The saddles 22A and 22B are in turn mounted on structural steel work supports 24.

The drum 10 serves as the water storaging and steamwater separating space of the unit. A steam-water mixture is delivered into thel drum 10 by the plurality of uniformly spaced risers 16, where the steam is separated by conventional means, such as centrifugal type separators, and passed to the steam outlet 26. Safety valve connections 28 and a vent nozzle 30 are also provided on the top of the drum. Gage glass connections 34, remote level indicator connections 35, a feed water inlet 36, and a chemical feed connection 38, are provided at one end of the drum. In the center bottom portion of the drum there is a blowdown nozzle 40.

Attached to the bottom portion of the drum 10 are a plurality of uniformly spaced downcomers 18 which, as shown in Fig. 2, bend outwardly from the centerline of the drum and then inwardly in an aligned formation 'into a plane coincidental with the longitudinal centerline of the drum, with the tubes then entering the shell of the heat exchanger 14 along the bottom thereof at uniformly spaced positions. Also attached to the bottom portion v of the drum 10 at the outer side of the downcomer tubes is a plurality of riser pipes 16 which also bend outwardly from the centerline of the drum beyond the outer limits of the heat exchanger, thence downwardly and inwardly tpfenter the heat exchanger at uniformly 'spaced positions valiangthe top thereof.

-In Figs.,v 3 to 8y isV shown the heat exchanger section 14 of `the: steanr 'generator which comprises an outer clon# gated pressure shell 42 of circular cross-section which is formed in a U-shape and having parallel legs 43 and 45 nxectedby a bight section 47. In the outer end of the shell leg 43Lis` Welded to the shell 42 a thick inlet tube sheet4 44 andiat a corresponding location in the leg 45 an outlet: tube sheet 46. A hemispherical pressure head 48 forming a heating fluid inlet chamber 50 is welded to the tube sheet 44 and -a corresponding hemispheric'al head 52 welded to the "outlet-tube sheet 46 to form a heating fluid outlet chamber 54. There is a large diameter inlet nozzle SiiV formed in the inlet head 48 and a correspondingly single `outlet nozzle 58 n the outlet head 52. Disposed within the shell '42 is a bundle of small diameter long bore parallel arranged U-tubes 60 forming the heat exchanger heat transfer surface. The 'opposite ends of the tubes 60 aresecured to the inlet tube sheet 44 and to the outlet tube sheet 46, so that there lis formed a continuous uid flow path from the inlet chamber through the tubes 60 tothe outlet chamber 54. The downcomers 18 tire uniformly spaced along the bottom of the heat exchanger 14 and connected to discharge the water to be evaporated through lthe feed inlets 62 indicated in Fig. 3. 'Ilhe water is partly evaporated as it passes upwardly hcrss the tubes and a steam 'and water mixture discharges from outlets 64 into corresponding uniformly spaced riseriflt.: inspection ports 66 are provided in the bight section 47 to allow X-raying vof the nal Weld of the hetfexchanger. Inspection and repair access openings v68 alsofprovided on both the inlet and the outlet hemispherical heads 48 and 52.

The tube bundle 60 is `arranged with the tubes on an quilateral pitch spacing, with `the tubes substantially and uniformly filling Vthe transverse cross-section of the pressure shell 42,"as'shownfin Figs. 4and 6. The distribution of the tubes of the tube bundle 60 is constant so as to present a transverse vcross-section which is uniform at all positions along the entire length of the heat exchanger 14'betw`eenthe tube sheets 44 and 46. As shown in Fig. 4 the 'tubes are supported in the shell legs 43 and '45 by pass'irrgthr'ou'gh corresponding slightly oversize holes '69 in Asupport'plat'es 70. Each Lplates 70, which has a cut out portion 71 at the top and bottom thereof for fflow qualization, iis vmounted concentric witlh shell 42 on spacer `bars 72. Each Vbar 72 is Vwelded to the shell and basa `recessed l:portion 74 into which the support plate 70 lits. A retaining bar 77 then vholds the lplat'e vin locked position. 'As'shown'inFigs 6 and 7, the tube pattern and general crosssectionin the bight section 47 ofthe exchanger vis the'same as thatintheshell legs 43 and45. Thetubes, however, are supported in a structure which permits linear expansion'of the tubes of the tube bundle 60 relative to thez'shell. This structure has a support ring 75 which en'ompasses'the tube bundle and which is mounted conce'nfrically within the vshell42 on 'spacer blocks 76 and on 4r`a load pedestal 78. The spacer blocks are welded Vto theri'ng 75 and slideon the shell 42. Transversely of the tubes and having their outer ends welded to the ring -75 are support bars 80 for each tube row, yeach located in a plane parallel vto the direction of thermal expansion gfthetubes of the bundle 60. The bars 80 support and vertically space the tubes with alternate bars being disposed aud welded to the ring -75 on opposite sides thereof.. The bottom bar'82 stands on its thin edgelto present @greater `resistance to bending. In the lowermost portion o'lflthe'exchanger a portion of the ring 75A is removed. hellowerbar A82 being welded torthe ring 75 carries the leutire''lo'a'diof 'thetube`bundle"60. This l'od'is dis'- 4 tributed to the shell by the two distributing bars 84 and 86 which are welded to the 4ring and bar structure. The load pedestal 78 is Welded to the shell 42 and on it the bar 86 slides While transmitting the load of the tube bundle 60. This arrangement allows the tubes to freely expand in the horizontal or expansion plane -with the tubes being restrained and supported in the transverse or vertical plane. The ring and bar support structure is free to deflect within itself to accommodate unusual d ifferential thermal expansions, and is not secured to the shell but only rests thereon. This structure thus completely and flexibly supports the tube bundle within the shell 42.

The heat exchanger shell 42 is designed to withstand the steam pressure of the steam generator `and is preferably constructed of high tensile strength carbon steel. This steel when in the presence of boiling water which is chemically maintained at a pH of 11.5 and with an oxygen content of less than .0l cc. per liter, will not substantially corrode 'during the design life of the heat exchanger. The tube sheets 44, 46 and hernispherical heads 52, 48 are also fabricated from high tensile strength carbon steel and are designed to withstand the operating pressure of the hot iluid in the chambers 50, 54. The pressure of the hot fluid may be of the order of 1500 to 3500 p.s.i. and the tube sheet 38" Vdiameter and 8" thickness. Tube sheets of this size must be capable of being fabricated with precision yand most importantly must have a high resistance 'to vcracking under severe temperature fluctuations. All of these features carbon steel possesses, 'to `a marked degree. Heating fluid temperature iluctuations of the order of 25 F. in ve seconds may safely occur in the described construction.

When the heating fluid, eg. pressurized water at a temperature of 500 to 650 F. circulated from the cooling system of -a high rate heat generating device by a high pressure .pump (not shown), is corrosive and must be vlr'naintained at a high purity, it is imperative that a chemically inert surface be in contact with the hot fluid throughout 'its ilow path. To this end the invention involves the vuse 'fof austenitic stainless steel cladding to cover the interior surfaces of the hemispherical heads 48, 52, 'the :faces 51, /53 'of 'the tube sheets 44, 46 and the provision of austenitic stainless steel U-shaped tubes. As "indicated infFig. 8, vthe tubes of the tube bundle 60 are secured in the unit by having their end portions expanded into the tube sheets 44 and 46 and their ends seal Welded directly to Y'the austenitic stainless steel cladding 88 of the'tube sheet on the hot fluid `faces 51, 53, by the method of welding disclosed and claimed in a copending application of O. R. Carpenter, Serial No. 405,959, tiled January 25, 1954. Thus there is a strong mechanical tube attachment plus welds between similar materials, i;e. -aus'tenitic stainless steel, assuring little likelihood of leakage between the hot Huid and the heated fluid.

The stainless steel internal cladding of the inlet and outlet chambers, tube sheets of the heat exchanger, and thethinwall stainless steel tubes provides complete assurance that the hot fluid will maintain its purity, thus making it Vpossible to fabricate Vthe thick walled pressure carrying members of the heat exchanger from suitable lowcost `carbon steel. This large use of carbon steel results in va major reduction in the cost of the heat exchanger.

v'Ihe provision of a U-tube bank and U-shaped shell, substantially eliminates anyl thermal expansion stress concentrations "and resultant .heat exchanger distortion. The provision of a heaty exchanger having a uniform cross-section throughout its length makes possible the realization'ot'maximumheat transfer effectiveness from everysquare foot ofhea't surface. This generalcongurationofheat exchanger when coupled with a series of uniformly spaced longitudinally distributed downcomer and riser fc'onne'c'tions, provides a single hot ud .pass ''n'd c'ool`uid'sngl`e`pass Yheat exchanger of maximum effectivness, mechanical integrity and minimum space requirements.

The longitudinal disposition of an elongated vaporliquid drum and the longitudinal disposition of the U- shaped heat exchanger with a plurality of downcomer and risers spaced uniformly along the length of said drum and heat exchanger provides a steam generator which requires a low circulation head height while maintaining a high circulation rate and allows the heat eX- changer and drum to be independently supported, with the differential expansion therebetween being taken by iiexible downcomers and risers connected therebetween.

While in accordance with the provisions of the statutes, we have illustrated and described herein a specific form of the invention now known to us, those skilled in the art will understand that changes may be made in the form of the apparatus disclosed without departing from the spirit of the invention covered by our claims, and that certain features of the invention may sometimes be used to advantage without a corresponding use of other features.

We claim:

1. A vapor generating unit comprising an upper elongated horizontally arranged vapor-liquid separating drum, a lower shell and tube type heat exchanger arranged for vapor generation elongated in a horizontal plane and having a tube bundle therein with the longitudinal centerline of the tubes parallel to the plane of elongation of said shell, means for passing a heating iiuid through the tubes of said heat exchanger, a vaporizable Huid circulation system connecting said separating drum and heat exchanger for high circulation rates of liquid ilow through the heat exchanger to provide partially evaporated liquid to said separating drum, said circulation system including a plurality of unheated vapor-liquid riser and liquid downcomer conduits connecting said separating drum and heat exchanger for the circulation of the vaporizable liquid through said heat exchanger and drum, said riser and downcomer conduits being connected at spaced positions along the top and bottom respectively of the length of said heat exchanger and at spaced positions along the length of said drum to provide a flow path of the vaporliquid mixture within said shell substantially transverse to the tubes therein.

2. A vapor generating unit comprising an upper elongated horizontally arranged vapor-liquid separating drum, a lower shell and tube type heat exchanger arranged for vapor generation elongated in a horizontal plane and having a tube bundle therein with the longitudinal center-line of the tubes parallel to the plane of elongation of said shell, means for passing a heating Huid through the tubes of said heat exchanger, a vaporizable iluid circulation system connecting said separating drum and heat exchanger for high circulation rates of liquid flow through the heat exchanger to provide partially evaporated liquid to said separating drum, said circulation system including a plurality of unheated vapor-liquid riser and liquid downcomer conduits connecting said separating drum and heat exchanger for the circulation of the vaporizable liquid through said heat exchanger and drum, said riser and downcomer conduits being connected at uniformly spaced positions along the top and bottom respectively of the length of said heat exchanger and at uniformly spaced positions along the length of said separating drum, to provide a flow path of the vapor-liquid mixture within said shell substantially transverse to the tubes therein, means for directly supporting said drum, separate means for directly supporting said heat exchanger independently of said dnum, and said riser and downcomer conduits being of a size and shape permitting exible expansion and contraction thereof without transferring prohibitive expansion stresses to said drum and heat exchanger.

3. A vapor generating unit comprising an upper elongated vapor-liquid separating drum disposed in a horizontal plane, a loiwer shell and tube type heat exchanger arranged for vapor generation comprising a U-shaped shell and U-shaped tubes contained therein disposed with the shell in a horizontal plane below said drum, means for passing a heating liuid through the U-shaped tubes of said heat exchanger, a vaporizable fluid circulation system connecting said separating drum and heat exchanger for high circulation rates of liquid flowl through the heat exchanger to provide partially evaporated liquid to said separating drum, said circulation system including a plurality of unheated vapor-liquid riser and liquid downcomer conduits connecting said idrum and heat exchanger for the circulation of the vaporizable liquid through said heat exchanger and separating drum, said riser1 and downcomer conduits being connected at uniformly spaced positions along the top and bottom respectively of the length of said heat exchanger and at uniformly spaced positions along the length of said drum to provide a flow path of the vapor-liquid mixture within said shell substantially transverse to the tubes therein.

4. A vapor generating unit comprising an upper elongated Vapor-liquid separating drum disposed in a horizontal plane, a lower shell and tube type heat exchanger arranged for vapor ygeneration comprising a U-shaped shell and U-shaped tubes contained therein disposed with said shell in a horizontal plane below said drum, means for passing a heating duid through said heat exchanger, a vaporizable lluid circulation system connecting said separating drum and heat exchanger for high circulation rates of liquid tlow through the heat exchanger to provide partially evaporated liquid to said separating drum, said circulation system including a plurality of nnheated vapor-liquid riser and liquid downcomer conduits connecting said drum and heat exchanger for the circulation of the vaporizable liquid through said heat exchanger and separating drum, said risers spaced along the top length of and said downcomers spaced along the bottom length of said shell to provide a ow path of the vaporliquid mixture within said shell substantially transverse to the tubes therein, means for directly supporting said drum, separate means for directly supporting said heat exchanger independently of said drum, and said riser and downcomer conduits being of a size and shape permitting flexible expansion and contraction thereof without transferring prohibitive expansion stresses to said drum and heat exchanger.

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